This invention relates to a filter cleaning arrangement particularly, but not only, suited for high efficiency particulate air ("HEPA") filters.
HEPA filters include a fiberglass paper medium arranged in relatively deep, narrow pleats separated by corrugated support members. Such filters are extremely efficient, and have been used extensively in sophisticated applications such as nuclear plants. They are, however, coming into increasing use in more conventional industrial applications such as in connection with chipping, grinding or cutting operations where it is desired to remove particulates from air in order to meet EPA and OSHA standards. Conventional baghouse systems do not filter effectively enough to meet such standards, and as a result the filtered air cannot be re-circulated in the plant and must be exhausted outside. This can result in substantial energy losses since the exhausted air must be replaced and heated or cooled to meet desired plant conditions, and it can also result in undesirable external emissions of particulate material.
HEPA filters must be cleaned or replaced like other filters, but they are relatively expensive so that frequent replacement is simply not financially feasible, particularly in conventional industrial applications. Conventional cleaning arrangements involve either blowing air through the filter from its outlet side or drawing air through it from its inlet side. Blowing air into a pleated filter is inefficient since this merely scatters the dust particles causing them to be entrapped in some other portion of the filter medium. On the other hand, using only a suction device creates a very localized cleaning force which is ineffective to clean into the depths of the filter pleats. Therefore, neither blower nor suction devices alone are capable of developing uniform pressure differentials for cleaning, particularly in a deeply pleated filter. As a result, it is necessary to use very large and expensive blower or suction units that can at some points create pressure differentials large enough to cause physical damage to the filter medium.